Haem: Blood Transfusions 1 Flashcards
What proportion of population are RhD negative?
15%
What type of antibodies are anti-RhD?
IgG
Therefore can cross the placenta
Describe how the consequences ABO incompatibility are different to rhesus incompatibility.
- ABO - immediated haemolytic transfusion reaction (can be fatal)
- Rhesus - delayed haemolytic transfusion reaction
Why does rhesus incompatibility cause delayed haemolysis?
Because IgG-binding leads to extravascular haemolysis
IgG activates complement less that IgM
List some other antigens that can lead to transfusion reactions.
- Rhesus C, c, E, e
- Kell (K), Duffy and Kidd (particularly important for delayed transfusion reactions)
What is a dangerous consequences of rhesus incompatibility in a pregnant woman?
Haemolytic disease of the newborn
How is the patient’s blood group tested?
- Anti-A, anti-B and anti-D reagents are mixed with the patient’s red blood cells
- A positive result means that the red cells will float to the top of the vial (agglutination)
Takes 10 minutes - done before every transfusion
How can the types of red blood cell antibodies in the patient’s serum be identified?
Known A and B group red blood cells are mixed with the patient’s plasma (which contains IgM antibodies)
Describe how the antibody screen of a patient’s plasma works.
- Conducted using the indirect antiglobulin test (IAT)
- 2 or 3 reagent red blood cells are used which contain all the important red cell antigens
- The patient’s serum is incubated with these screening cells
- Anti-human immunoglobulin is added to the solution which allows briding of red cells that are coated with IgG
- This results in the formation of a visible clump
- This is a group and screen
What labels are included on issued blood?
ABO and RhD status
Other Rh antigens and K
Which patient group should receive K negative blood?
Women of childbearing potential
What is a full crossmatch?
- Uses indirect antiglobulin test
- Patients plasma is incubated with DONOR red cells at 37 degrees for 30-40 mins
- Anti-human immunoglobulin is added to allow cross-linking of antibodies
- Formation of a clump would suggest that antibodies against donor red cell antigens are present in the patient’s plasma
Not suitable in emergencies due to because it take 40 minutes
What is an immediate spin?
- Incubate patient’s plasma and donor red cells for 5 mins and spin
- This will only detect ABO incompatibility
- Used in emergency situations
- IgM anti-A or anti-B will bind to donor RBCs, fix complement and lyse cells
What is an electronic crossmatch?
- Also called electronic issue (EI)
- Compatibility is determined by an IT system without physical testing of donor cells against plasma
How it is done now in modern era - quick, requires fewer staff and allows better stock management
How long do red cells survive in storage?
35 days in 4 degrees
How soon after leaving storage do red cells need to be transfused?
4 hours
NOTE: red cells can be returned to the fridge within 30 mins of leaving storage
Describe how platelets are cross-matched.
They do NOT need cross-matching because the antigens are weakly expressed
Which antigens are important when considering fresh frozen plasma transfusion?
Only ABO
If group O blood is given to A, B or AB patients, what precaution should you take?
Do not use high titre blood (i.e. blood that does not contains high levels of anti-A and anti-B antibodies)
What is the universal donor for:
- Red blood cells
- Plasma
- Red blood cells = O negative
- Plasma = AB (contains no anti-A or anti-B antibodies)
Why do platelets have a shorter shelf-life than red blood cells?
They are stored at room temperature so they are more likely to get contaminated by bacteria
What should you do if a patient receiving a platelet transfusion develops a fever?
- Stop the platelets and take blood cultures
- Platelets should be sent back to the lab for microbiological testing
If a patient develops a reaction to a plasma transfusion, what is the most likely cause?
Allergic reactions
NOTE: plasma is frozen so it is unlikely to get contaminated by bacteria
List some indications for RBC transfusion.
- Major blood loss - if >30% blood lost
- Peri-operative care - if Hb <70g/dL
- Post-chemotherapy - if Hb <80g/dL
- Symptomatic anaemia - ischaemic heart disease, breathless
By how much would 1 unit of RBC increase the haemoglobin leel in a 70kg patient?
10 g/L
If a group and screen is performed and no antibodies are present, is a crossmatch necessary?
No
List some methods of transfusing your own blood.
- Pre-operative autologous deposit (not available in the UK)
- Intra-operative cell salvage (blood is collected during surgery, centrifuged, filtered and reinfused)
- Post-operative cell salvage (blood that is lost post-operative is collected via a wound drain, filtered and re-infusd - usually for orthopaedic operations)
NOTE: all coagulation factors and platelets are removed in cell salvage
Which patient groups would cell salvage be used for?
- Patients with rare blood groups
- Jehovah’s witnesses
Which patient groups require CMV-negative blood?
- For intra-uterine and neonatal transfusions
- Elective transfusion in pregnancy
Which patients require irradiated blood and why?
Highly immunosuppressed patients
- These patients cannot destroy donor lymphocytes and the presence of lymphocytes in donated blood can cause transfusion associated graft-versus-host disease
Which patients require washed blood?
- Patients who have severe allergic reactions to donors’ plasma proteins
- This takes 4 hours so must be requested in advance
NOTE: IgA deficient patients are more likely to need washed blood
List some indications for platelet transfusions.
- Massive transfusion - aim for >75 x 10^9/L
- Prevent bleeding (post-chemotherapy) - if <10 x 10^9/L
- Prevent bleeding (surgery) - if <5 x 10^9/L
- Platelet dysfunction or immune cause - only if actively bleeding
List some contraindications for platelet transfusion.
- Heparin-induced thrombocytopaenia
- TTP
By what level will 1 unit of platelets increase the platelet count in a 70 kg adult?
30-40 x 10^9/L
List some indications for FFP transfusion.
- Massive transfusion
- DIC (if bleeding or invasive procedure)
- Liver disease
What does FFP contain?
All the coagulation factors
What is the adult dose of FFP?
15 mL/kg
4 units
How many mLs is 1 unit of FFP?
250mL
Patients usually given 4 units
What is the best option for the reversal of warfarin?
Prothrombin complex concentrate (contains 2, 7, 9 and 10)
What does cryoprecipitate contain?
- Fibrinogen
- FVIII and vWF
- Fibronectin
- FXIII
- Platelet microparticles
- IgA
- Albumin
What is the most common blood type?
O positive (1/3 of donors)
